Effects of Fe dopants and residual carbonates on the catalytic activities of the perovskite-type La_0.7Sr_0.3Co_1-xFe_xO₃ NO_x storage catalyst

Herein, we reported the NO_x storage capacity, NO oxidation ability and sulfur resistance of the La_0.7Sr_0.3CoO₃-based perovskite-type catalysts. NO could be readily oxidized to NO₂ with around 83% of NO-to-NO₂ conversion at 300°C over the perovskite. After sulfation, the NSC of the La_0.7Sr_0.3CoO₃ catalyst calcined in static air decreased 58.0%. Nevertheless, a significant improvement of the sulfur tolerance could be achieved through partial substitution of Co with Fe cations, as well as calcination in flowing air. The NSC of the pre-sulfated La_0.7Sr_0.3Co_0.8Fe_0.2O₃ catalyst maintained 360.7μmol/g and dropped only 6.4% as compared with the fresh one. The XPS results confirmed the presence of Fe₂(SO₄)₃ in the sulfated La_0.7Sr_0.3Co_0.8Fe_0.2O₃ catalyst. The EXAFS results further revealed that the formation of Fe₂(SO₄)₃ in the perovskite inhibited the sulfation of neighboring strontium from the viewpoint of the local atomic level. These findings strongly suggest that the La_0.7Sr_0.3Co_0.8Fe_0.2O₃ perovskite is a possible NO_x absorber used for aftertreatment systems upon lean-burn engines with the advantages of the excellent NO oxidation ability, NO_x storage capacity and the high sulfur tolerance.